ifnotfound

Ifnotfound is a general term in software development referring to a mechanism for supplying a fallback value when a lookup or retrieval fails to find a requested item. It is not a fixed keyword in all languages, but many systems implement equivalent behavior with different syntax, often by returning a default or fallback value.

In programming, if a key or item is missing from a data structure, a default is typically provided. Examples include using a dictionary lookup that returns a default when the key is absent, or employing constructs like optional chaining with a nullish coalescing operator to supply a substitute when a value cannot be found. In templates and rendering engines, similar patterns ensure that a renderable value appears even if the source data is incomplete.

In databases and data queries, functions such as COALESCE or IFNULL serve a related purpose: they return a specified default when an expression evaluates to NULL or is otherwise unavailable. In configuration and search contexts, an ifnotfound option may specify what to display, log, or trigger when a resource cannot be located, contributing to resilience and user experience.

Considerations include selecting appropriate defaults, handling localization, and avoiding the masking of missing data where explicit absence is meaningful. Performance considerations may arise if multiple fallbacks are evaluated; using caching or sensible early exits can mitigate overhead. The concept is widely used across programming languages and frameworks, with syntax and exact behavior varying by context, but the core idea remains consistent: provide a sensible substitute when a lookup fails.